It’s Fourth of July weekend! In a flurry of holiday weekend domestication, I cleaned the apartment for our house guest and made a cake on Friday. If only baking didn’t lead to such yummy, but equally fattening food, then I’d bake every day.
I am a sucker for those cake pans sold by Williams Sonoma (but can be found for less at Kitchen Kapers and The Christmas Tree Shop) that are in crazy shapes. We have a snowman, Santa Claus, gingerbread house, and the one I used yesterday: a rose shaped pan.
Of course, all those small ridges and details inside the pan are wonderful places for cakes to get stuck. We made the gingerbread house last year and ended up having to cut the cake from the pan and completely ruining the dessert. While complaining about its problems and yet still wanting to buy another version of these pans, a clerk at Kitchen Kapers suggested melting Crisco and using a brush to grease the pans before filling it.
We tried this immediately to beautiful results (I highly recommend!) so I repeated on Friday to equally excellent results. The hard part now is cleaning the small bowl of melted Crisco and brush. I originally tried putting the brush under the running water and working the Crisco out with my fingers. Instead of washing away, the Crisco coated my fingers, the brush, and solidified in a horrid mess.
Crisco doesn’t like water. AT ALL.
Why is that? Why does oil form small droplets in water instead of mixing together? Where did we ever get the phrase about oil and water not mixing?
Chemistry!
Broadly speaking, molecules can be broken into two groups: hydrophilic or hydrophobic. Hydrophilic literally means “water loving,” while hydrophobic is “water fearing.”
Let’s start with water since everything else seems to either love it or hate it.
Figure 23.1 shows a picture of a water molecule. For several reasons that I won’t go into now, water has two ends that are positively charged and one end that is negatively charged. Think of a water molecule as a magnet with positive and negative poles.
Hydrophilic molecules also have ends that are positively and negatively charged.
What do magnets do? Their positive ends attract other negative ends and these ends hold tightly together.
If you want to wash away hydrophilic molecules from something you are cleaning, all you need is some water. The negative and positive ends of water will match up with the negative and positive ends of the hydrophilic molecule. The two are now stuck together and both will run down the drain (Figure 23.2).
However, there is still the whole other class of molecules: hydrophobic ones. These molecules are different from water in that they don’t have positive or negative ends. They are instead neutral in charge and thus have no attraction to water. Think about placing a magnet on a piece of wood. It won’t stick, will it?
If hydrophilic molecules like other hydrophilic molecules, what do hydrophobic molecules like?
Other hydrophobic molecules, of course! Examples of hydrophobic molecules: oil, butter, Crisco!
Because oil is very hydrophobic, it has no interest in water and would much rather hang out with itself. In fact, it hates water so much that will arrange itself so it has the most minimal contact with water it can possibly have. This is why oil forms droplets in water.
So, does this mean that we should be washing our clothes with a mixture of water and oil? The water would remove hydrophilic molecules and the oil would remove the hydrophobic ones?
I’m sure you can see that perhaps this isn’t the best course of action. You’d be making quite the mess of your clothes if they were dipped in any amount of oil.
The answer to this little problem is soap. Soaps are molecules that have hydrophilic ends and hydrophobic ends. Their hydrophobic ends will get together with other hydrophobic molecules around and stick together. Their hydrophilic ends will attach to other hydrophilic molecules and water allowing everything to be washed away (Figure 23.3).
I quickly realized that the best way to get the Crisco out my brush was to cover the thing in soap. I worked the soap into the bristles then rinsed under running water. My hands and the brush were free of Crisco in minutes.
Have a safe and happy holiday weekend!
Here’s my rose-shaped cake! (Yes, I already took out a slice…)
Hydrophilic: literally meaning "water loving," these molecules have positive and negative ends capable of interacting with water molecules.
Hydrophobic: literally meaning "water fearing." these molecules are very neutral and have no ability to interact with water. In fact, these molecules highly dislike water and won't mix.
Soap: a molecule that has both a hydrophilic end and a hydrophobic end. The hydrophilic end can interact with water while the hydrophoic end will interact with other hydrophobic molecules. Soaps are wonderful at cleaning because they can interact with both kinds of molecules.
Zumdahl, Steven S. “Chemical Principles, 4th Edition” (2002) Houghton Mifflin Company, Boston, MA.
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